Motor driven vehicles have considerably more power than that required under normal operating conditions. However these excess power reserves are required for abnormal operating conditions such as high driving speeds and maintaining proper driving speed when negotiating grades. It is also desirable to have additional power reserves to accelerate in traffic situations where lack of available acceleration would otherwise result in an accident.
The availability of this power is however frequently misused to accelerate vehicles from a starting position or from low speeds to higher speeds at excessive rates. This unnecessary acceleration contributes very substantially to the fuel consumption in stop and go or varying speed traffic conditions common to city driving. In some cases the use of the excess power by the driver has resulted in a 25% increase in fuel consumption.
Standard arrangements of vehicle or engine controls and instrumentation are not suitable to overcome this problem. Governors or warning devices for total engine power, engine RPM, engine throttle setting or fuel supply to the engine are unsuitable because they restrict the available power when it is required in the abnormal conditions mentioned above. This also applies to the system in which the engine intake manifold vacuum gauge is used as a simple warning device indicating uneconomical fuel wastage as a result of the vacuum being low due to the throttle being opened too much at low engine RPM.
Acceleration and deceleration measuring or warning devices based on inertia or gravity principals have been proposed for controlling both positive and negative vehicle acceleration. However, due to their very nature, they are inherently disadvantageous due to the fact that they are subject to gravity and as such do not function properly when the vehicle is climbing or descending a grade in the road. Furthermore, because they are essentially mechanical, they are also adversely affected by shocks or vibrations to the vehicle resulting in activation of these inertia and gravity systems under non-acceleration situations.
The present invention overcomes the difficulties of the prior art by providing an acceleration warning system comprising differentiating means for determining the rate of acceleration change of the vehicle and means responsive to a predetermined output of the differentiating means for indicating when the acceleration of the vehicle is beyond a predetermined rate. The system may be used to indicate positive acceleration, negative acceleration or deceleration, or both acceleration and deceleration.
Unlike previous systems, the present invention is strictly dependent upon the acceleration of the vehicle. It therefore permits the use of the power reserves when required in abnormal driving conditions, such as climbing steep grades and pulling heavy loads, since the use of the power reserve under these conditions does not produce an excessive increase in acceleration.
According to an aspect of the invention, the system includes electrical speed measuring apparatus providing a DC voltage proportionate to the speed of the vehicle a differentiation circuit providing a voltage corresponding to the rate of change of vehicle acceleration, and switch means operated by a predetermined output from the differentiator circuit to activate warning and/or control means for warning and/or controlling of excessive acceleration. The switch means may include a first limit switch responding to a first predetermined output voltage from the differentiating circuit relating to positive acceleration and a second limit switch responding to a second predetermined output from the differentiating circuit relating to a negative acceleration or deceleration.
The control means may be in the form of an automatic control activated by the switch means for limiting or restricting the supply of fuel to the engine when the rate of acceleration exceeds a desired or recommended rate. The fuel control is arranged to allow only minimal acceleration and no acceleration whatsoever beyond the recommended rate.